Preheat oven to 350 degrees and spray a muffin tin with non-stick spray.
Pour milk and vinegar into a small bowl, stir to combine and set aside for 5 minutes.
Combine flax meal and water in a small bowl, stir to combine and set aside for 5 minutes.
Add corn meal, flour, baking soda, coconut sugar and salt to a large bowl. Stir to combine.
Add agave, pumpkin, vegan butter, flax meal mixture, milk mixture to the bowl. Stir to combine.
Dice 1 jalapeño and fold into the batter.
Distribute batter among 12 muffin tins. Top each muffin with a jalapeño slice and press it down slightly.
Bake for 18-20 minutes, or until a toothpick comes out clean.
Serve warm with vegan butter.